Kerry told members of the House Foreign Affairs Committee that they face a choice between an agreement that will curb Iran's nuclear program and impose strict inspections, or no deal at all. If the US walks away from the agreement, Kerry says America's international partners will not follow.
But he says it will be harder to push back against a nuclear-armed Iran.
House Republicans oppose the deal and Rep. Eliot Engel, the top Democrat on the committee, suggested that the deal might just be pushing the "pause button" on Iran getting a nuclear weapon for 15 years.